The present disclosure relates generally to radio frequency communication systems. In particular although not exclusively the present disclosure relates to an apparatus for measuring sources of interference.
Quality of Service (QOS) is of major importance to today's communication network providers. One of the major factors effecting QOS in most modern communication is interference. The two most appreciable forms of interference present in most communication systems result from Active and Passive intermodulation. In each case multiple transmitting frequencies combine in ways that cause interference to receiving equipment.
In the case of Active Intermodulation (AIM) interference the transmitter or receiver actively amplify interfering signals in the environment that cause harmful interference. Passive Intermodulation (PIM) interference is similar to active intermodulation interference except that it almost occurs exclusively in passive elements when two or more frequencies are simultaneously present. When signals F1 and F2 for example encounter a non-linear device they combine as follows, mF1±nF2, (m,n=1,2,3 . . . ) to produce interfering signals.
To date most suppliers of RF communications components have not been able to model PIM. One can only design components to reduce the possibility of significant levels of PIM being internally generated. Typically this reduction is achieved by applying lessons learnt from past experiences, and from testing the component presently under design. While it is possible to take account for PIM produced by each individual component during the system design phase, the effects of PIM which can be generated outside the components via poor interconnects etc, and when the component are installed on-site cannot be so easily accounted for.
Presently it has been relatively difficult to test for PIM on-site. Historically the equipment required to perform the testing was rather large and cumbersome and not readily suited for in-field deployment and has been widely considered by most in the communications industry as being impractical. Typically such on-site PIM testing requires each junction, line and interconnect to be checked. Without a PIM tester on-site, this operation is extremely labour intensive, requiring a technician to physically check/remake each connection as installed, and as such is extremely costly.